Ford Motor Co. and Chrysler Group LLC overcame a quirk in the industry sales calendar to post surprise U.S. gains for September while future growth may be challenged by the government shutdown that began today.

The 17% surge in U.S. auto sales last month pushed the annual rate to a pre-recession, boom-time level. Even more significant, Detroit automakers are reaping profits not seen since the turn of the century.

Ford Motor Co. and Chrysler Group LLC, leading a continued recovery for the U.S. auto market, said their deliveries climbed in June as the industry selling pace may accelerate to the fastest pace in 66 months.